1. Field of the Invention
The present invention relates to a technique of transmitting audio information via a wide area network.
2. Description of the Related Art
The Internet telephony (IP telephony) by the VoIP (Voice over IP) technique has been used to establish voice communication on the Internet and other IP (Internet Protocol) networks. The VoIP technique receives and transmits audio information converted into IP packets via the IP network to establish voice communication. Standardization of H.323 as the protocol of the VOIP technique enhances the interconnection of the Internet and the telephone line. The IP telephony has gradually been spread through replacement of internal lines and exclusive lines in a diversity of enterprises and organizations.
The IP telephony requires the baud rate of about 20 kbps for communication of audio information, and applies greater loading to the communication line, compared with the general data communication. The communication line of the lower baud rate causes deterioration of the telephone speech quality. The IP telephony uses a gatekeeper to register the addresses of terminals as communication targets, except in the case of directly inputting each IP address to specify and call a desired communication target. The IP telephony also uses a gateway to establish connection of the IP telephony line with the subscriber phone line. Namely the communication line ensuring the sufficient telephone speech quality and the additional equipment including the gatekeeper and the gateway are essential for the enhanced convenience of the IP telephony. The IP telephony accordingly has additional expenses apart from the general connection fees for the service provider to the Internet. The users of the IP telephony are requested to pay for such expenses.
An IP telephony system utilizing the IP network is disclosed in, for example, PATENT LAID-OPEN GAZETTE No. 2002-125069.
The high total communication expenses due to the additional cost and the difficulty in construction of the good charge system interfere with the further spread of the IP telephony. One available measure uses advertisement to attain the low-cost or free telephone service. But no effective techniques have been proposed so far with regard to addition of the advertisement to the IP telephony system. Because of the characteristics of the IP telephony, addition of the advertisement requires all the data in the IP telephony system to pass through a specific server used for addition of advertisement information. This is against the fundamental advantages of the Internet. The construction of making all the data pass through the specific server applies extremely heavy loading to the server and causes congestion of the line.